Triassic origin and early radiation of multicellular volvocine algae
Triassic origin and early radiation of multicellular volvocine algae
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DOI：
10.1073/pnas.0811205106
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发表时间：
2009-03-03
影响因子：
11.1
通讯作者：
Michod, Richard E.
中科院分区：
文献类型：
--
作者：
Herron, Matthew D.;Hackett, Jeremiah D.;Michod, Richard E.
个体的进化转变（eti）是地球生命史上分水岭事件的基础，包括细胞、真核生物、植物、动物和真菌的起源。这些事件中的每一个都构成了复杂性水平的增加，因为个体群体在他们自己的权利中成为个体。在研究得最好的外星生物之一是绿藻中多细胞的起源，这是一个多细胞进化和细胞分化的模型系统。自其从单细胞祖先分化出来以来，团藻已进化成具有细胞特化、复杂发育程序和细胞间高度协调的高度整合的多细胞生物。值得注意的是，所有这些变化都被认为发生在过去的5000万到7500万年之间。在这里，我们使用多基因数据集和多个化石校准来估计分化时间，并使用这些估计来推断与多细胞进化相关的发育变化的时间。我们的研究结果表明，团藻至少在2亿年前从单细胞祖先中分化出来。合作、冲突和冲突调解的早期周期产生的两个关键创新导致了这一群体中多细胞形式的迅速整合和辐射。这是唯一一个有详细时间表的ETI，但多层次选择理论预测，类似的变化一定发生在其他ETI中。
Evolutionary transitions in individuality (ETIs) underlie the watershed events in the history of life on Earth, including the origins of cells, eukaryotes, plants, animals, and fungi. Each of these events constitutes an increase in the level of complexity, as groups of individuals become individuals in their own right. Among the best-studied ETIs is the origin of multicellularity in the green alga Volvox, a model system for the evolution of multicellularity and cellular differentiation. Since its divergence from unicellular ancestors, Volvox has evolved into a highly integrated multicellular organism with cellular specialization, a complex developmental program, and a high degree of coordination among cells. Remarkably, all of these changes were previously thought to have occurred in the last 50-75 million years. Here we estimate divergence times using a multigene data set with multiple fossil calibrations and use these estimates to infer the times of developmental changes relevant to the evolution of multicellularity. Our results show that Volvox diverged from unicellular ancestors at least 200 million years ago. Two key innovations resulting from an early cycle of cooperation, conflict and conflict mediation led to a rapid integration and radiation of multicellular forms in this group. This is the only ETI for which a detailed timeline has been established, but multilevel selection theory predicts that similar changes must have occurred during other ETIs.